Field of the Invention
The present invention relates to isolated polypeptides having glucoamylase activity and isolated polynucleotides encoding the polypeptides. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods for producing and using the polypeptides, and to uses of glucoamylases of the invention and a process for producing a liquefaction, saccharification and/or fermentation product using the glucoamylase of the present invention. The present invention also relates to a composition comprising a glucoamylase of the invention.
Description of the Related Art
Glucoamylase (1,4-alpha-D-glucan glucohydrolase, EC 3.2.1.3) is an enzyme, which catalyzes the release of D-glucose from the non-reducing ends of starch or related oligo- and poly-saccharide molecules. Glucoamylases are produced by several filamentous fungi and yeast, with those from Aspergillus being commercially most important.
Glucoamylases (equivalent to amyloglucosidase, AMG) are mostly sold as saccharification enzymes to various industries including brewing, starch and fuels. In starch and fuel industries, glucoamylases are commercially used to convert starchy material, which is already partially hydrolyzed by an alpha-amylase, to glucose. The glucose may then be converted directly or indirectly into a fermentation product using a fermenting organism. Examples of commercial fermentation products include alcohols (e.g., ethanol, methanol, butanol, 1,3-propanediol); organic acids (e.g., citric acid, acetic acid, itaconic acid, lactic acid, gluconic acid, gluconate, lactic acid, succinic acid, 2,5-diketo-D-gluconic acid); ketones (e.g., acetone); amino acids (e.g., glutamic acid); gases (e.g., H2 and CO2), and more complex compounds, including, for example, antibiotics (e.g., penicillin and tetracycline); enzymes; vitamins (e.g., riboflavin, B12, beta-carotene); hormones, and other compounds which are difficult to produce synthetically. Fermentation processes are also commonly used in the consumable alcohol (e.g., beer and wine), dairy (e.g., in the production of yogurt and cheese), leather, beverage and tobacco industries.
The end product may also be syrup. For instance, the end product may be glucose, but may also be converted, e.g., by glucose isomerase to fructose or a mixture composed almost equally of glucose and fructose. This mixture, or a mixture further enriched with fructose, is the most commonly used high fructose corn syrup (HFCS) commercialized throughout the world.
The purification and properties of two forms of glucoamylase from Penicillium oxalicum were disclosed (Yoshiki YAMASAKI, Agric. Biol. Chem., 41 (5), 755˜762, 1977). Both glucoamylases were stable at up to 55° C., but at temperature around 60° C., the glucoamylase activities dropped sharply. The sequences of the two forms of glucoamylases were not disclosed in this article or even later publications.